Suhua Wang

Field emission from crystalline copper sulphide nanowire arrays

Straight crystalline copper sulphide (Cu2S) nanowire arrays have been grown by using a simple gas–solid reaction at room temperature. These were demonstrated to exhibit semiconductor properties. Field emission was observed at a field of ∼6 MV/m, and its current-field characteristics deviate from Fowler–Nordheim theory, i.e., showing a nonlinear Fowler–Nordheim plot. The uniform emission from the whole arrays was observed using transparent anode technique, and their variation with applied field was recorded. The emission from individual nanowires was also studied using a field emission microscope, and was found to consist of a number of spatially resolved diffuse spots. Finally, stable emission current at different levels and over time was recorded. These findings indicate that semiconductor nanowires as cold cathode have a potential future, worthy of further comprehensive investigation. The technical importance of using semiconductor nanowires as cold cathode emitter is given.

Surfactant-assisted growth of crystalline copper sulphide nanowire arrays

A novel method for growing crystalline CuxS nanowires on an oxidized copper surface is reported, which is based on the surfactant-assistance. The nanowire is shown to consist of a monoclinic core Cu2S and a tetragonal shell Cu1.96S. Under appropriate conditions, straight and uniform nanowires can be grown, which are up to 30 μm long and a few tens nanometers thick.

Thermal oxidation of Cu2S nanowires: A template method for the fabrication of mesoscopic CuxO (x = 1,2) wires

The thermal behavior of Cu2S nanowires has been studied in the presence of N2 and O2. The nanowires are stable in N2 at the highest temperature we have studied (320 °C), but they are oxidized by O2 to Cu2O above 260 °C and to CuO at even higher temperatures. At the highest temperature we have studied (400 °C), the S atoms in the Cu2S nanowires are completely removed by O2, forming CuxO wires mainly with x = 2. Although the Cu1,2O wires are polycrystalline and are much thicker than Cu2S nanowires, they are remarkably uniform. This represents a new template method for the synthesis of mesoscopic Cu1,2O wires.

Phase transitions in the Cu2S nanowires

Phase transitions in the Cu-2-S nanowires have been studied as a function of temperature and pressure. Differential scanning calorimetry (DSC) shows an endothermic process at 101.8degreesC upon heating, corresponding to the phase transition from gamma-Cu2S (monoclinic) to beta-Cu2S (hexagonal) in the bulk (103.5degreesC). However, the reverse phase transition was found to be much lower (74.8 degreesC). X-ray diffraction (XRD) demonstrates that the c-axis of gamma-Cu2S is transformed to the c-axis of beta-Cu2S owing to the positional disorder of the Cu atoms. Two high-pressure phases of Cu,S have been identified using a diamond anvil cell and the energy-dispersive XRD technique

The crystal structure and growth direction of Cu2S nanowire arrays fabricated on a copper surface

We examine the crystal structure and growth direction of Cu2S nanowire arrays grown from copper surfaces at room temperature. By using X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction (ED) techniques, the monoclinic Cu2S nanowires are shown to grow preferentially along the c-axis, characterized by a layered structure. This result may shed light on the unusual growth mechanism of the Cu2S nanowires.

Oxide-assisted nucleation and growth of copper sulphide nanowire arrays

Abstract Highly oriented and uniform-sized Cu 2 S nanowire arrays grown on copper substrates have been studied by high-resolution transmission electron microscopy. Cu 2 S nanowires consist of single crystalline cores of Cu 2 S and polycrystalline Cu 2 O shells. Most Cu 2 S nanowires have a similar crystalline orientation and their growth directions were [0 0 1] Cu 2 S as determined by electron diffraction and HRTEM. The orientation relationship between Cu 2 S crystalline core and Cu 2 O crystals in the shells was determined to be (1 0 0) Cu 2 S ∥(1 1 0) Cu 2 O and [0 1 0] Cu 2 S ∥〈1 1 1〉 Cu 2 O . The nucleation and growth process of Cu 2 S nanowires were interpreted by oxide-assisted growth mechanism.

One-dimensional growth of rock-salt PbS nanocrystals mediated by surfactant/polymer templates*

A novel method has been developed for the synthesis of compound semiconductor nanorods (PbS). This method consists of using a functionalized lead(II) salt Pb(AOT)2 as the precursor and a polymer (PVB) as both a matrix and a stabilizer. The PbS nanocrystallites prepared using this method are all oriented with their (100) lattice planes parallel to the substrate surface. Possible mechanisms are briefly discussed for the growth of the rod-shaped PbS nanocrystals with the preferred orientation in the polymer film.

Spectroscopic characterization of the copper sulphide core/shell nanowires

Abstract Cu 2 S/Cu 1.96 S core/shell nanowires were characterized by X-ray photoelectron spectroscopy (XPS), UV–VIS absorption spectroscopy and electron paramagnetic resonance spectroscopy (EPR). Preliminary results revealed the characteristic atomic compositions and spectroscopic properties of the Cu x S nanowires.

CHARACTERIZATION OF SEMICONDUCTOR QUANTUM DOTS

The applications of various optical and electrical characterization techniques to the study of semiconductor quantum dots (QDs) are summarized. Photoconductivity enhancement effect in CdS-PVK nanocomposite is studied by optical absorption, photoluminescence (PL), photoconductivity spectroscopy, and time-resolved PL. It is found that the photoconductivity of the composite is greatly enhanced in comparison with that of a simple mixture of CdS nano-particles and PVK. PL spectra have shown that luminescence from PVK is dramatically quenched by the incorporation of a low density of CdS particles. Time-resolved spectra reveal that the decay of the PL from the dots of the composite in much longer than that in the simple mixture. These have been attributed to a fast carrier transfer mechanism between CdS QDs and PVK matrix. In addition, optical properties of PVP-capped ZnO QDs are investigated in details. Typical PL spectra of PVP-capped ZnO QDs consist of a sharp UV peak located at about 3.45 eV and a broad green emission band centered at 2.34 eV. At certain Zn2+/PVP ratios the green emission band is quenched and only strong UV emission remains. This effect is attributed to the surface modification of ZnO quantum dots with PVP. We are able to associate the UV emission from ZnO QDs to localized states by applying temperature and excitation power dependent PL. Finally, the electronic level of molecular beam epitaxy grown self-organized ZnSe QDs embedded in ZnS is determined by applying PL, capacitance-voltage measurement, and deep level transient spectroscopy.